Active steering systems and methods for marine seismic sources

ABSTRACT

Systems and methods for automatic steering of marine seismic sources are described. One system comprises a marine seismic spread comprising a towing vessel and a seismic source, the seismic source comprising one or more source arrays each having a center of source array, each source array having one or more source strings; a seismic source deployment sub-system on the towing vessel, the sub-system controlled by a controller including a software module, the software module and the deployment sub-system adapted to control an inline distance between one of the centers of source array and a target coordinate. It is emphasized that this abstract is provided to comply with the rules requiring an abstract, allowing a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to the field of marine seismic dataacquisition systems and methods of using same. More specifically, theinvention relates to systems and methods for active steering of marineseismic sources to maintain inline position of the seismic sources.

2. Related Art

The performance of a marine seismic acquisition survey typicallyinvolves one or more vessels towing at least one seismic streamerthrough a body of water believed to overlie one or morehydrocarbon-bearing formations. In order to perform a 3-D marine seismicacquisition survey, an array of marine seismic streamers, each typicallyseveral thousand meters long and containing a large number ofhydrophones and associated electronic equipment distributed along itslength, is towed at about 5 knots behind a seismic survey vessel. Thevessel also tows one or more seismic sources suitable for use in water,typically air guns. Acoustic signals, or “shots,” produced by theseismic sources are directed down through the water into the earthbeneath, where they are reflected from the various strata. The reflectedsignals are received by the hydrophones, or receivers, carried in thestreamers, digitized, and then transmitted to the seismic survey vesselwhere the digitized signals are recorded and at least partiallyprocessed with the ultimate aim of building up a representation of theearth strata in the area being surveyed. Often two or more sets ofseismic data signals are obtained from the same subsurface area. Thesesets of seismic data signals may be obtained, for instance, byconducting two or more seismic surveys over the same subsurface area atdifferent times, typically with time lapses between the seismic surveysvarying between a few months and a few years. In some cases, the seismicdata signals will be acquired to monitor changes in subsurfacereservoirs caused by the production of hydrocarbons. The acquisition andprocessing of time-lapsed three dimensional seismic data signals over aparticular subsurface area (commonly referred to in the industry as“4-D” seismic data) has emerged in the last decade or so as an importantnew seismic prospecting methodology. When conducting repeated surveys,ideally one wants to repeat all source and receiver positions from thebase or previous survey. In practice, this is hard to achieve for theentire survey area due to the different environmental conditionsencountered in different surveys. Varying currents, both spatially andin time, are the main environmental contributor.

When conducting surveys today, a reference point at the vessel issteered automatically to be at a certain cross line distance from agiven pre-plot track. A controller may be used for this, and it controlsthe autopilot mechanism to achieve its goal. The operator sets manuallyhow far the vessel is to be cross-line from the pre-plot line.Conventionally, seismic source arrays are deployed so that fixeddistances are maintained from the towing vessel and from the center ofthe first seismic recording group of the streamers. During the course ofan acquisition line, these distances may change due to several factorsincluding crossline current that introduces an angle to the relationbetween the line from the towing cable/rope and the seismic linedirection, often called feather angle when used to describe the samerelation but for streamers. In addition to crossline feather, changes inthe inline component of the current may alter the tension on the towingropes for individual source arrays, which may then stretch or contract,changing the distances from the vessel to the to the source arrays, andfrom the source arrays to the center of the first seismic recordinggroup.

While adjustments may be made during line change, no mechanism iscurrently employed to control these separation distances in real timeduring the course of a marine seismic data acquisition run. This lack ofcontrol may result in inline differences between the source coordinatesfrom a base and monitor 4D survey.

SUMMARY OF THE INVENTION

In accordance with the present invention, systems and methods aredescribed for inline positioning of one or more acoustic centers ofmarine seismic sources using control of one or more source deploymentcomponents on a vessel. Systems and methods of the invention may be usedduring seismic data collection, including 3-D and 4-D seismic surveying.The inventive systems and methods may also use inline, as well ascrossline control to reform a multi-string source shape in real time ornear-real time, and/or for time recording with time and space sourcefiring. In another use of the invention, the ability to move the sourceinto position using both control of the vessel speed and inline sourcecontrol makes it possible to conduct an undershoot without the sourcevessel receiving the aim point message. Data transfer that is not timecritical can be achieved with the limited bandwidth available fromsatellite communications eliminating the need and cost for a dedicatedline of sight radio effort. Normally, in an undershoot project, the lineof sight is needed for transmitting the aim point message from therecording vessel to the source vessel. Instead the vessels shoot ontime, with highly synchronized and precise clocks.

The systems and methods of the present invention may include a softwaremodule that has knowledge of the inline source positions in relation totarget coordinates from a previous survey and an ongoing acquisition.One objective of the software is to control one or more sourcedeployment components that can change the position of one or moresources in relation to the towing vessel in a way that will drive thedifference between these two inline coordinates to zero. The softwaremay also have knowledge of a target distance between the center firstgroup (CFG) of a streamer spread and the center of the source (COS)and/or the center of one or more source arrays (COSA) and control thephysical mechanism to achieve that target distance. This of courserequires that the positions of both the CFG and the COS or COSA, as thecase may be, are known.

The systems and methods of the invention may include one or more sourcedeployment components controlled by the software module. Acting inconcert, the software module and source deployment components controlthe inline distances of the COSA of each array in relation to a targetcoordinate, which may be either reference mentioned above, (i.e., thebase survey source coordinates or the distance between a COS of a sourcearray and CFG of a streamer spread). One useful source deploymentcomponent is the so-called gun cable winch. A gun cable winch winds andunwinds a pneumatically pressurized cable from the source towing vesselto the source array (gun cables) in or out, changing the distance fromthe winch to the source array. Gun cable winches are not typicallydesigned to change the length of gun cable dynamically duringacquisition when the cables are pressurized.

A first aspect of the invention are systems comprising:

-   -   (a) a marine seismic spread comprising a towing vessel and a        seismic source, the seismic source comprising one or more source        arrays each having a center of source array, each source array        having one or more source strings;    -   (b) a seismic source deployment sub-system on the towing vessel,        the sub-system controlled by a controller including a software        module, the software module and the deployment sub-system        adapted to control an inline distance between one of the centers        of source array and a target coordinate.

Systems of the invention include those wherein optionally one or moreseismic streamers are towed by the towing vessel, or a separate towingvessel may tow one or more streamers. The seismic source deploymentsub-system may comprise one or more winches, capstans, or the like, forexample a port side winch and a starboard side winch, controlled by thecontroller software module. In these embodiments, the individual sourcestrings in a source array are actuated pneumatically or electronicallythrough individual active cables wound or unwound from winches. The portwinch may be wound a substantially similar amount as the starboard sidewinch is unwound, or vice versa. Alternatively, the source deploymentsub-system may comprise both active source cables and passive steeringcables. In one embodiment, the length of active source cables are notcontrolled but are allowed to move inline, while a set of separatepassive cables are connected either to the active cables or the sourcesthemselves. The passive cables do not actuate the sources, but theirinline lengths are controlled by separate deployment systems, forexample winches, to control an inline distance between one of thecenters of source array and a target coordinate. In certain embodiments,the seismic source deployment sub-system may be load-balanced, whereinfor example port and starboard winches are controlled to moveoppositely. In certain embodiments, the source deployment sub-system maycomprise movable winches, wherein the winch does not wind or unwind perse, but rides on a movable platform. Combinations of these may also beemployed, in other words, the controller and software module may controlboth the movable platform and the winding and unwinding of the winches.In yet other embodiments, heave compensators may be employed, wherebythe length of either active source cables or passive steering cables areadjusted by exerting a force on the cable out of line of the cable, asexplained further herein. Load-balancing may be employed in any of thevarious embodiments of the invention, which may reduce energyconsumption.

The controller and software module may be physically a part of theseismic source deployment sub-system or located separately from theseismic source deployment sub-system, and may use some or all availableinformation, including, but not limited to, source and vessel positions,vessel gyroscope reading, vessel compass reading, vessel speed log,streamer front end positions (if streamers are present), and historical,real-time, and future current and wind information and predictions whencalculating a difference between a target position and actual position,and thus these may taken into consideration in the calculation ofoptimum source cable and/or steering cable position by the seismicsource deployment sub-system. The phrase “seismic source deploymentsub-system” is defined herein and may differ among the variousembodiments of the invention, as explained in the definition. Thecontroller and software module may include logic selected from PIcontrollers, PID controllers (including any known or reasonablyforeseeable variations of these), and computes a residual equal to adifference between a target point 3D coordinate COSA position and anactual COSA position, optionally together with current and windmeasurements, to produce one or more inputs to cable deploymentactuator, which may be electric motors, used by the seismic sourcedeployment sub-system to control the source inline positions usingwinches, motorized capstans, and the like. The controller may computethe residual continuously or non-continuously. Other possibleimplementations of the invention are those wherein the controllercomprises more specialized control strategies, such as strategiesselected from feed forward, cascade control, internal feedback loops,model predictive control, neural networks, and Kalman filteringtechniques.

Systems of the invention may include a seismic spread comprising one ormore vessels such as towing vessels, a chase vessel, a work vessel, oneor more a seismic sources, and optionally one or more seismic streamerstowed by towing vessels. The streamers and sources may be separatelytowed or towed by the same vessel. If towed by separate vessels, twocontrollers may be employed and two residuals computed. In general, thecontroller may compute the residual based on what the positionmeasurement system reports as the 3D coordinate position of the trackingpoint. Although there may be some degree of error in the reported 3Dcoordinate position due to a variety of error sources, includinginstrument measurement error, even with the errors the tracking pointmay be better controlled by steering the vessel the majority of thetime.

Systems and methods of the invention may optionally be used inconjunction with other systems and methods. For example, if the centerof source is the tracking point, its 3D coordinate position may bedetermined from acoustic ranging networks, GPS, and other positionsensors, and since the seismic team knows the path the tracking point issupposed to follow based on the survey specifications, the controllermay use at least that information to calculate a residual, and a setpoint based on the residual, for the steering algorithm, either to steerthe vessel back to the survey-specified path, or ensure that thesurvey-specified path is adhered to.

Another aspect of the invention comprises methods of automaticallycontrolling an inline position of a center of a marine seismic source,comprising:

-   -   (a) measuring a position of a center of a marine seismic source        in a marine seismic spread;    -   (b) computing a residual difference between the measured        position and a target position of the center of source; and    -   (c) steering the source using a seismic source deployment        sub-system comprising one or more cables attached to the source,        the cable adjusted based on the residual difference.

Methods of the invention include those wherein the computing includesuse of a PI or PID controller alone or in conjunction with othercontrollers, and may comprise towing a seismic spread comprising atowing vessel, a seismic source, and one or more seismic streamers,which may be towed in side-by-side configuration, over/underconfiguration, “V” configuration, “W” configuration, or some otherconfiguration. Other methods of the invention rely not on controllingposition or steering of the sources, but in timing their firing tocompensate for inline skew caused by environmental and/or other factors.

Another aspect of the invention comprises adjusting firing times of thesource strings to distribute evenly any inline error due to un-even shotspacing in time or distance, rather than using mechanical actuators andcontrollers to correct for inline skew. One method comprises:

-   -   (a) deploying a marine seismic spread comprising a towing vessel        and a seismic source, the seismic source comprising one or more        source arrays each having a center of source array, each source        array having one or more source strings; and    -   (b) adjusting firing times of the source strings to distribute        evenly any inline error due to un-even shot spacing in time.

Systems and methods of the invention will become more apparent uponreview of the brief description of the drawings, the detaileddescription, and the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The manner in which the objectives of the invention and other desirablecharacteristics can be obtained is explained in the followingdescription and attached drawings in which:

FIGS. 1 and 2 are plan or overhead views of a system useful indescribing ideal conditions, and problems addressed by the systems andmethods of the invention;

FIGS. 3, 4, and 5 are schematic block diagrams of three embodiments ofsystems and methods of the invention;

FIGS. 6A and 6B are schematic diagrams of a feature of the inventivesystems and methods, where FIG. 6A is partially in phantom;

FIGS. 7, 8, 9, and 10 are schematic block diagrams of four otherembodiments of systems and methods of the invention;

FIG. 11 illustrates schematically another method of the invention; and

FIG. 12 illustrates is an image from an analysis of an actual seismicdata survey, showing all the shots from that particular survey as dots,and illustrating the influence from external forces (e.g. currents) oninline skew.

It is to be noted, however, that the appended drawings are not to scaleand illustrate only typical embodiments of this invention, and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details and that numerous variations ormodifications from the described embodiments may be possible. Forexample, in the discussion herein, aspects of the invention aredeveloped within the general context of controlled positioning ofseismic spread elements, which may employ computer-executableinstructions, such as software program modules, being executed by one ormore conventional computers. Generally, software program modules includeroutines, programs, objects, components, data structures, etc. thatperform particular tasks or implement particular abstract data types.Moreover, those skilled in the art will appreciate that the inventionmay be practiced in whole or in part with other computer systemconfigurations, including hand-held devices, personal digitalassistants, multiprocessor systems, microprocessor-based or programmableelectronics, network PCs, minicomputers, mainframe computers, and thelike. In a distributed computer environment, software program modulesmay be located in both local and remote memory storage devices. It isnoted, however, that modification to the systems and methods describedherein may well be made without deviating from the scope of the presentinvention. Moreover, although developed within the general context ofautomatically controlling position of seismic spread elements, thoseskilled in the art will appreciate, from the discussion to follow, thatthe principles of the invention may well be applied to other aspects ofseismic data acquisition. Thus, the systems and method described beloware but illustrative implementations of a broader inventive concept.

All phrases, derivations, collocations and multiword expressions usedherein, in particular in the claims that follow, are expressly notlimited to nouns and verbs. It is apparent that meanings are not justexpressed by nouns and verbs or single words. Languages use a variety ofways to express content. The existence of inventive concepts and theways in which these are expressed varies in language-cultures. Forexample, many lexicalized compounds in Germanic languages are oftenexpressed as adjective-noun combinations, noun-preposition-nouncombinations or derivations in Romanic languages. The possibility toinclude phrases, derivations and collocations in the claims is essentialfor high-quality patents, making it possible to reduce expressions totheir conceptual content, and all possible conceptual combinations ofwords that are compatible with such content (either within a language oracross languages) are intended to be included in the used phrases.

The present invention relates to various systems and methods forcontrolling position of seismic sources in a marine seismic spreadprimarily by steering the sources using a controller and sourcedeployment components, the latter being a vessel that tows the seismicsources. One aspect of the present invention relates to systemsincluding a seismic source deployment sub-system on the towing vessel,the sub-system controlled by a controller including a software module,the software module and the deployment sub-system adapted to control aninline distance between one of the centers of source array and a targetcoordinate. Another aspect of the invention comprises methods of using asystem of the invention to control the inline position of seismicsources. An alternative method of the invention comprises timing thefiring of seismic sources to compensate for inline skew.

As used herein a marine seismic “source” is a collection of air-guns orother acoustic devices designed to produce acoustic signals, or “shots,”which are directed down through the water into the earth beneath, wherethey are reflected from the various strata.

The phrase “center of source”, sometimes referred to herein as COS,means the 3D coordinate position of the center of a plurality ofacoustic devices making up a source. The COS may be the 3D coordinateposition of a single source array or multiple source arrays.

A “source array”, as used herein, refers to a plurality of acousticsignal-producing devices arranged generally in a rectangular grid andtowed by a vessel using one or more towing members, which may be activeor passive. In the case of active towing members, the towing membersalso function to communicate pneumatic, hydraulic, or electronic signalsto the individual acoustic devices in the source arrays to produce anacoustic shot. When speaking of “dual sources”, typically a port sourcearray and a starboard source array are used, and each source array has a“center of source array.” Each source array may have one or a pluralityof source strings, such as gun strings, and each source string may havea plurality of individual acoustic devices. Each source string may haveits own towing member, but the invention is not so limited.

The phrase “center of source array”, or COSA, is distinguished from COSonly when there are two or more source arrays, and means the 3Dcoordinate position of the center of a plurality of acoustic devicesmaking up a source array.

The phrase “streamer front end center”, sometimes referred to herein asSFC, means the 3D coordinate position of a plurality of streamer frontends determined from the individual 3D coordinate positions of eachstreamer front end, that is, the streamer ends closest to the towingvessel.

The phrase “seismic source deployment sub-system” means any device orcollection of components that are capable of functioning to position orsteer source arrays in order that the COSA of each source array may besubstantially aligned in a crossline generally perpendicular to a“preplot” line, or target vessel path. Seismic source deploymentsub-systems useful in the invention they may include components thatgenerate commands to elements, such as electric motors, winches,capstans, and other actuators, to accomplish the intended movements ofthe seismic sources. In some embodiments of the invention the seismicsource deployment sub-system may include one or more software programmodules, controllers, computers and the like, which may interact withvessel tracking and autopilots. In other embodiments of the inventionthe sub-system may not interact with conventional vessel tracking andautopilot functions, and may be simply one or more winches or capstansand associated controllers. In yet other embodiments of the invention,all of these components (tracking computer, autopilot, ruddercontroller, and thruster controllers) may be employed.

The term “spread” and the phrase “seismic spread” are usedinterchangeably herein and mean the total number of components,including vessels, vehicles, and towed objects including cables, sourcesand receivers, that are used together to conduct a marine seismic dataacquisition survey.

The term “control”, used as a transitive verb, means to verify orregulate by comparing with a standard or desired value. Control may beclosed loop, feedback, feed-forward, cascade, model predictive,adaptive, heuristic and combinations thereof.

The term “controller” means a device at least capable of accepting inputfrom sensors and meters in real time or near-real time, and sendingcommands directly to mechanical components, actuators, and the like, ofa seismic source deployment sub-system, and optionally to spread controlelements, and/or to local devices associated with spread controlelements able to accept commands. A controller may also be capable ofaccepting input from human operators; accessing databases, such asrelational databases; sending data to and accessing data in databases,data warehouses or data marts; and sending information to and acceptinginput from a display device readable by a human. A controller may alsointerface with or have integrated therewith one or more softwareapplication modules, and may supervise interaction between databases andone or more software application modules.

The phrase “PID controller” means a controller using proportional,integral, and derivative features, as further explained herein. In somecases the derivative mode may not be used or its influence reducedsignificantly so that the controller may be deemed a PI controller. Itwill also be recognized by those of skill in the control art that thereare existing variations of PI and PID controllers, depending on how thediscretization is performed. These known and foreseeable variations ofPI, PID and other controllers are considered within the invention.

The phrase “spread control element” means a spread component that iscontrollable and is capable of causing a spread component to changecoordinates, either vertically, horizontally, or both, and may or maynot be remotely controlled.

The terms “control position”, “position controllable”, “remotelycontrolling position” and “steering” are generally used interchangeablyherein, although it will be recognized by those of skill in the art that“steering” usually refers to following a defined path, while “controlposition”, “position controllable”, and “remotely controlling position”could mean steering, but also could mean merely maintaining position. Inthe context of the present invention, “control inline position” meansusing at least measured position of the COS or COSA and compare it to apre-plot path in order to give commands to the seismic source deploymentsub-system.

“Real-time” means dataflow that occurs without any delay added beyondthe minimum required for generation of the dataflow components. Itimplies that there is no major gap between the storage of information inthe dataflow and the retrieval of that information. There may be afurther requirement that the dataflow components are generatedsufficiently rapidly to allow control decisions using them to be madesufficiently early to be effective. “Near-real-time” means dataflow thathas been delayed in some way, such as to allow the calculation ofresults using symmetrical filters. Typically, decisions made with thistype of dataflow are for the enhancement of real-time decisions. Bothreal-time and near-real-time dataflows are used immediately after thenext process in the decision line receives them.

The term “position”, when used as a noun, is broader than “depth” orlateral (horizontal) movement alone, and is intended to be synonymouswith “spatial relation.” Thus “vertical position” includes depth, butalso distance from the seabed or distance above or below a submerged orsemi-submerged object, or an object having portions submerged. When usedas a verb, “position” means cause to be in a desired place, state, orspatial relation. The term may also include orientation, such asrotational orientation, pitch, yaw, and the like.

As previously discussed herein, when conducting time-lapse and othermarine seismic surveys using towed streamers and sources,conventionally, seismic source arrays are deployed so that fixeddistances are maintained from the towing vessel and from the center ofthe first seismic recording group of the streamers. During the course ofa marine data acquisition run, these distances may change due to severalfactors including crossline current that introduces an angle to therelation between the line from the towing cable/rope and the seismicline direction, often called feather angle when used to describe thesame relation but for streamers. In addition to crossline feather,changes in the inline component of the current may alter the tension onthe towing ropes for individual source arrays, which may then stretch orcontract, changing the distances from the vessel to the to the sourcearrays, and from the source arrays to the center of the first seismicrecording group. While adjustments may be made during line change, nomechanism is currently employed to control these separation distances inreal time during the course of a marine seismic data acquisition run.This lack of control may result in inline differences between the sourcecoordinates from a base and monitor 4D survey.

FIGS. 1 and 2 schematically illustrate a system and method useful fordescribing problems addressed by the inventive systems and methods.Illustrated in schematic plan view is a vessel 2 following a preplotline 4. The pre-plot line might be straight or have certain curvature.Vessel 2 is illustrated pulling two source arrays 6 and 8, each havingthree source strings. Source arrays 6 and 8 each have a center of sourcearray, or COSA, indicated by a star at 10 and 12, respectively. Sourcearray 6 is towed behind vessel 2 by a series of tow members 12, whilesource array 8 is towed by a series of tow members 14. Streamer frontend deflectors 16 and 18 help pull streamers 20 and 22 outward frompreplot line 4, with the help of tow members 24 and 26, respectively, aswell as separation ropes 28 and 30. Deflectors 16 and 18 may be of thetype known under the trade designation MONOWING™, available fromWesternGeco, LLC, Houston, Tex., or other type of streamer deflector.Those knowledgeable in the marine seismic industry will recognize manyvariations on the number of sources and streamers, configuration ofstreamers and tow members, and so on, and this is only one of manypossible foreseeable configurations which may benefit from the teachingsof the inventive systems and methods. In the arrangements illustrated,it is understood that sources and seismic streamers are towed at somedepth below the water surface. Sources are typically towed at depthsranging from 0 to 10 meters, while seismic streamers may be towed atmultiple depths, but are typically at depths ranging from 3 to 50meters, depending on the survey specifications.

Referring now to FIG. 2, the system of FIG. 1 is now exposed to an oceancurrent, wind, and/or waves represented by arrow 32. The same numeralsare used throughout to designate same components unless otherwisementioned. Vessel 2 must turn into the environmental conditions in orderto maintain a path close to preplot line 4. However, this action byvessel 2 results in inline skewing of the spread, and specificallyinline skew of COSAs 10 and 12 as represented by double-headed arrow 34.In 4D seismic data acquisition scenarios, this presents a problem,specifically that some percentage of the seismic data will not beuseful.

Prior to the systems and methods of the invention, the operator viewedthe source arrays and streamers, and perhaps took into considerationwind, wave and current data, in steering the vessel in an effort to keepthe streamers and the center of source on their respective track lines,while also minimizing inline skew. Systems and methods have been devisedto automate the steering feedback loop, by introducing an automaticcontroller that controls vessel position in such a way that the sourceis on or close to the desired preplot line; however, these systems donot account for inline skew as depicted schematically in FIG. 2. Thuseven if the source and streamers are on their respective preplot tracks,the COSAs may be experiencing inline skew. Systems and methods of theinvention are meant to correct for this inline skew. The systems andmethods of the invention may also utilize measurements of environmentalconditions, including but not limited to wind magnitude and direction,and current magnitude and direction. Other options include using afeed-forward technique, where a separate controller may be added thattakes these environmental conditions into account and performs aproactive reaction so as to minimize the environmental effect on thezero inline slew objective. If other factors are found to impact thezero inline skew objective, feed-forward control aspects from thesefactors may also be included. By performing these functionsautomatically, an optimally tuned PID and optionally a feed forward, orother controller strategy will command an algorithm within the seismicsource deployment sub-system so that deviations from the inline skewobjective is corrected rapidly and in a stable way.

FIGS. 3, 4, and 5 are schematic block diagrams of three non-limitingembodiments of systems and methods of the invention for controllinginline position of COSAs 10 and 12 in dashed line 40. FIG. 3 illustratesa system and method 300 for compensating for inline skew by dynamicallyactuating otherwise existing actuators, where three actuators 36 may beindependently and dynamically actuated, one for each of three port towmembers 12, while three other actuators 38 may also be independently anddynamically actuated for three starboard tow members 14. It will beunderstood that more or less than three actuator/tow member combinationsmay be employed. In this embodiment the actuators, which may be winchesor equivalent actuators, such as capstans, do not move in relation tovessel 2 other than to dynamically reel in and reel out the tow members,and operation of one actuator does not interact with the otheractuators. Operation of these types of actuators in marine seismic dataacquisition, other than the real time or near real time dynamic featuresof the invention, is well-known and requires no further explanation tothe skilled artisan. In certain embodiments, the dynamic reeling in andout of actuators 36 and 38 are automatically controlled in incrementalfashion by one or more controllers, each of which may comprise one ormore software program modules. The controller may comprise a simple PIor PID feedback loop. For example, a PID controller would compare a setpoint inline skew of COSAs 10 and 12 with measured 3D coordinatepositions of the COSAs, and calculate a difference, referred to hereinas a residual or residual difference, and generate a command toactuators 36 and 38 as the case may be to incrementally reel in or reelout the tow members 12 and 14. It will be understood that in certainembodiments, rather than the controllers sending commands directly toactuators 36 and 38, the controllers may send commands to a vesselautopilot, vessel tracking device, or both the tracking device andautopilot, and command the vessel rudder and/or vessel thrusters.However, in other embodiments, the response time of the actuators 36 and38 may be faster when the controllers send commands directly to theactuators to incrementally reel in and out the tow members, and correctfor inline skew of COSAs 10 and 12. In either case the result should bebetter control of COSAs 10 and 12 inline as depicted in dashed line 40.

FIG. 4 illustrates another system and method 400 for compensating forinline skew by dynamically actuating three actuators 36, one for each ofthree port tow members 12, while three other actuators 38 aredynamically actuated for three starboard tow members 14. In thisembodiment the actuators again do not move in relation to vessel 2 otherthan to dynamically reel in and reel out the tow members. However, inembodiment 400, actuators 36 and 38 are modified so that port andstarboard sides are synchronized. In other words, as actuators 36incrementally reel in tow members 13 because of environmental conditions32, a synchronizing connection 42 ensures that actuators 38incrementally reel out tow members 14. If environmental conditions 32were in the opposing direction, then as actuators 36 incrementally reelout tow members 13, synchronizing connection 42 ensures that actuators38 incrementally reel in tow members 14. Embodiment 400 allows loadbalancing through the synchronizing connection. Load balancing may beused in any of the embodiments of the invention, except embodiment 300of FIG. 3 which is a non-synchronized, non-balanced embodiment. Loadbalancing is primarily used to decrease energy requirements and/orincrease energy efficiency.

FIG. 5 illustrates another system and method embodiment 500 of theinvention in schematic block diagram fashion. System and methodembodiment 500 illustrated in FIG. 5 includes certain features notpresent in embodiments 300 and 400. In embodiment 500, actuators 36 and38 may once again be three port and three starboard winches,respectively, but each actuator 36 and 38 is movable forward and aft ona movable platform (not shown) controlled by one or more controllerscommanding movements of a mechanism 44. Mechanism 44 as illustrated inFIG. 5 may comprise a motorized capstan or other suitable arrangementhaving a connection to each movable platform associated with actuators36 and 38. In certain embodiments, one movable platform is employed forthree winches, and in embodiment 500, two movable platforms are thusutilized, although the invention is not so limited. Alternatively, eachactuator 36 and 38 may be controlled by its own motorized capstan. Asdepicted in FIG. 5, mechanism 44 allows load balancing as discussedherein, although this is optional. Actuators 36 and 38 may travel ontracks or rails, for example, as discussed in U.S. Pat. No. 5,284,323with regard to laterally movable reels for streamer deployment. Althoughthis patent discusses tracks for laterally moving reels for streamers,some of the principles are applicable to the inventive systems andmethods. Actuators 36 and 38 may be winches movably attached to andcapable of traversing forward and aft in separate tracks on the deck ofvessel 2. Separate traversing motors and chains may provide one meansknown to those skilled in the art to effect the traversal of actuators36 and 38 over these tracks. Traversing motors may cause chains torotate over a course along the length of each track, while the winchesor reels may ride on a frame (not shown) mounted on wheels that engagethe tracks. The frame may be connected to an element of chain such thatas the chain circles, winch 36 or 38 as the case may be is carriedforward and aft by means of the rolling of the frame wheels over thetrack. Other equivalent means for effecting the traversal of an actuatorover a track will be well known and recognized by those skilled in theart. For instance, a rod with left and right spiral grooves could becaused to rotate. The frame could be attached to an element that rideswithin the grooves of the rod such that when the rod is rotated, theelement causes the winch to be urged forward or aft.

FIGS. 6A and 6B are schematic diagrams of a feature of the inventivesystems and methods which may be used with any of the variousembodiments. Inline compensation may be supplemented by adding optionalport and starboard heave compensators. A starboard compensator isillustrated schematically in side elevation, partially in phantom, inFIG. 6A, employing a first, stationary wheel 46 and a second, slack takeup wheel 48. As tow member 14 is reeled in and out, or even when in astatic position, the heaving up and down of vessel 2 by wave action,wind, or other environmental factors, may cause tow member 14 toexperience slack, which can adversely result in inline skew of COSAs 10and 12. A pivot 50 and mounted pivot arm 52 allows slack take up wheel48 to pivot as indicated by the double-headed arrow. The phantomposition of pivot arm 52 and wheel 48 illustrates a situation when thereis relatively no heave. FIG. 6B illustrates schematically how gears 54and 56 may be employed in conjunction with a starboard pivot 50 and aport pivot 58 for rotation in opposite directions and load balancing.

FIG. 7 illustrates schematically another embodiment 700 where inaddition to actuators for tow members 13 and 14, separate extraactuators 60 and 62 are provided. In certain embodiments, one extraactuator is provided for each tow member 13 and each tow member 14. Inembodiment 700 illustrated schematically in FIG. 7, six extra actuators(winches, capstans, or the like) are provided, along with three extratow members 64 and three extra tow members 66. Extra tow members 64terminate at and are attached to, in this embodiment, the lead end ofeach acoustic string in sub-array 6. Similarly, extra tow members 66terminate at and are attached to, in this embodiment, the lead end ofeach acoustic string in sub-array 8.

Embodiment 800 of FIG. 8 combines features of embodiment 700 of FIG. 7with embodiment 500 of FIG. 5. In embodiment 800, extra actuators 68 and70 may once again be three port and three starboard winches,respectively, but each extra actuator 68 and 70 is movable forward andaft on a movable platform (not shown) controlled by one or morecontrollers commanding movements of a mechanism 72. Mechanism 72 asillustrated in FIG. 8 may comprise a motorized capstan or other suitablearrangement having a connection to each movable platform associated withextra actuators 68 and 70. In certain embodiments, one movable platformis employed for three winches, and in embodiment 800, two movableplatforms are thus utilized, although the invention is not so limited.Alternatively, each extra actuator 68 and 70 may be controlled by itsown motorized capstan. As depicted in FIG. 8, mechanism 72 allows loadbalancing as discussed herein, although this is optional. Extraactuators 68 and 70 may travel on tracks or rails, for example, asdiscussed in embodiment 500, or any other suitable arrangement. Theresult is better control of inline skew of COSAs 10 and 12 in the dashedline designated 40.

FIG. 9 illustrates another embodiment 900 of systems and methods of theinvention. In embodiment 900, all twelve actuators (three port acousticsource string actuators (not shown), three starboard source stringactuators (not shown), three extra port actuators 62 for tow members 66,and three extra starboard actuators 60 for tow members 64) aresynchronized. Port and starboard extra actuators 60 and 62 are operatedso that one side gives out while the other side takes in theirrespective tow members 64 and 66.

FIG. 10 illustrates yet another system and method embodiment 1000, whichis identical to embodiment 700 of FIG. 7 except for the terminalconnection point of tow members 64 and 66. In embodiment 1000 towmembers 64 and 66 are connected near midpoints of respective tow members13 and 14, but this location of connection may vary, depending on thedegree of control required, the forces required, the expectedenvironmental conditions, the physical characteristics of tow members 64and 66 (such as strength, elasticity, and the like), and other factors.

Controllers useful in the invention may be Model Predictive (MP)controllers rather than PID controllers. The characteristics of each arediscussed herein below. MP controllers may be mono-variable ormultivariable MP controllers, and may use a pre-existing mathematicalmodel of the system in conjunction with measured disturbances on thesystem, such as wind, currents, and the like, to calculate residuals andgenerate commands. Modification of set points by a feed-forwardcontroller may optionally feed historical, real time or near-real time,or future predictions of data regarding current and/or wind as amodification to set points. In either embodiment, steering of sourcestrings will then influence the inline skew in a more controlled andstable fashion using an MP controller and feed-forward controller,rather than an MP controller alone, or a human operator.

As should now be evident, using the systems and methods of the inventionthe operator does not have to perform manual control, and this mayresult in:

-   -   an objective reaction not dependent on operator skill level and        alertness;    -   control reaction with little or no delay;    -   proactive response to current and other environmental factors        with feed forward options; and    -   more frequent update rates.

The systems of the invention may be used in conjunction withconventional crossline spread control devices. These devices includesource steering devices and streamer steering devices. Such devices areoften part of the spread and towed by the vessel.

Controllers useful in the systems and methods of the invention may varyin their details. One PID controller useful in the invention may beexpressed mathematically as in Equation 1:u(t)=K _(p) [e(t)+1/T _(i) ·∫e(t)dt+T _(d) −è(t)]  (1)

wherein:

-   -   ∫ means integrate;    -   è(t) means the time derivative;    -   u(t) is controller output to an actuator, typically measured in        meters of inline skew;    -   e(t) means difference between wanted (planned, reference) inline        position and measured (current position) inline value;    -   T_(d) is a constant for describing the derivative part of the        algorithm (the derivative part may be filtered to avoid deriving        high frequencies);    -   T_(i) is a constant for describing the integrating part of the        algorithm; and    -   K_(p) is a proportional gain constant.

In the s-plane (Laplace), the PID controller may be expressed as(Equation 2):H _(r)(s)=K _(p)[1+1/T _(i) s+T _(d) s/(1+T _(f) s)]  (2)

wherein:

-   -   is the variable in the s-plane; and    -   T_(f) is a constant describing the filtering part of the        derivative part of the algorithm.

For discretization, a variety of transforms may be employed, and someconstants may or may not be useful. For example, the T_(f) constant maynot be necessary in some instances, but may be especially useful inother scenarios. As one discretization example, the z-transform may beused, meaning that the integral part of the algorithm may beapproximated by using a trapezoid model of the form (Equation 3):s=(1−z ₋₁)/T  (3)

while the derivative part may be approximated using an Euler model(Equation 4):s=2/T·(1−z ₋₁)/(1+z ₋₁)  (4)

wherein T is the sampling time.

The resulting discrete model may then be used directly in the steeringalgorithm. Other discrete models, derived using other transforms, areuseful in the invention, and will be apparent to control technicians orcontrol engineers of ordinary skill.

Model Predictive Control (MPC) is an advanced multivariable controlmethod for use in multiple input/multiple output (MIMO) systems. Anoverview of industrial Model

Predictive Control can be found at:www.che.utexas.edu/˜qin/cpcv/cpcv14.html. MPC computes a sequence ofmanipulated variable adjustments in order to optimise the futurebehavior of the process in question. At each control time k, MPC solvesa dynamic optimization problem using a model of the controlled system,so as to optimize future behavior (at time k+1, k+2 . . . k+n) over aprediction horizon n. This is again performed at time k+1, k+2 . . . MPCmay use any derived objective function, such as Quadratic PerformanceObjective, and the like, including weighting functions of manipulatedvariables and measurements. Dynamics of the process and/or system to becontrolled are described in an explicit model of the process and/orsystem, which may be obtained for example by mathematical modeling, orestimated from test data of the real process and/or system. Sometechniques to determine some of the dynamics of the system and/orprocess to be controlled include step response models, impulse responsemodels, and other linear or non-linear models. Often an accurate modelis not necessary. Input and output constraints may be included in theproblem formulation so that future constraint violations are anticipatedand prevented, such as hard constraints, soft constraints, set pointconstraints, funnel constraints, return on capital constraints, and thelike. It may be difficult to explicitly state stability of an MPCcontrol scheme, and in certain embodiments of the present invention itmay be necessary to use nonlinear MPC. In so-called advance spreadcontrol of marine seismic spreads, PID control may be used on strongmono-variable loops with few or nonproblematic interactions, while oneor more networks of MPC might be used, or other multivariable controlstructures, for strong interconnected loops. Furthermore, computing timeconsiderations may be a limiting factor. Some embodiments may employnonlinear MPC. Mono-variable or multivariable model predictivecontrollers could substitute for one or more of the PID controllers invarious embodiments.

Feed forward algorithms, if used, will in the most general sense be taskspecific, meaning that they will be specially designed to the task it isdesigned to solve. This specific design might be difficult to design,but a lot is gained by using a more general algorithm, such as a firstor second order filter with a given gain and time constants.

All embodiments of the invention may include a modification of the setpoint signal by a feed-forward controller, which may optionally feedhistorical, real time or near-real time, or future predictions of dataregarding currents, wind, and other environmental conditions orinformation regarding obstructions in the designated survey area, andthe like.

FIG. 11 illustrates another method of the invention, comprisingadjusting firing times of the source strings to distribute evenly anyinline error due to un-even shot spacing in time or distance, ratherthan using mechanical actuators and controllers to correct for inlineskew. FIG. 11 illustrates the point of un-even shot spacing in time ordistance, showing two sources 10 and 12 at three different times t1, t2,and t3. The center of vessel 2 is indicated at 3. For repeat surveysthat aim to repeat the source positions from the base survey, this is ofcourse also a major problem, as it will be very difficult to match theinline component of the source positions if the source feathering of thesubsequent survey does not match the source feathering experienced inthe base survey. Another factor to consider is that the chance ofoverlapping shots (two shots fired into the same shot record) is reducedif the shot interval (in time) is increased. This could be done byadjusting the vessel speed in order to:

-   -   1. maximize efficiency (i.e. vessel moves as fast as possible,        around ˜5 knots, or 2.5 m/s); and    -   2. avoid overlapping shots.

FIG. 12 is an image from an analysis of an actual seismic data survey.It shows all the shots from that particular survey as dots. If there hadbeen no influence from external forces (e.g. currents) and the vesselhad been steering straight, all the dots would have been found on point(0,−175), as the source was towed 175 m behind the vessel for thisparticular survey. As can be seen, however, due to currents pushing thesource array to the sides (mostly to port side), the inline error wasincreased (exceeding 40 m in the extreme cases). If there are nocrossline currents causing source feather, the vessel speed could beadjusted to maximize efficiency of data collection. In a dual sourcearrangement, as soon as crossline current starts to affect the inlinedistance between the center of the two sources, the shot controller maybe programmed to try to compensate by adjusting the firing times. Aslong as there is no shot overlap, the vessel speed may remain constant.If the source feather increases to a point where there is a chance ofoverlapping shot records, the system decides whether to slow the vesseldown, or to freeze the triggering times (i.e. no further adjustment) toavoid overlapping shots. (The decision on which to choose may vary fromsurvey to survey).

Un-even shot spacing in time or distance may be partially fixed byadjusting firing times, and using the geometric mid-point between thesources to distribute the error evenly, as depicted in FIG. 11. Althoughnone of these techniques can fully compensate for inline skew, thetechnique illustrated in FIG. 11 has been implemented in an existingshot controller. The implementation is, however, not straightforward.FIG. 11 illustrates an example with a record shot length of 6.0 seconds,a nominal shot spacing of 18.75 m; a vessel speed of 5 knots, or 2.5m/s; source layback of 300 m; and a source feather of 5°. For theseconditions, it can be shown that the inline skew is about 4.35 m. It wasfound that if the shot time period was held constant at 7.5 seconds, andthe shot spacing distance was varied as 14.4 m-23.1 m-14.4 m -23.1 m,the inline skew could be reduced without significant shot overlap. If,rather than varying the shot spacing distance, the shot spacing distanceremained constant at 18.75 m, and the shot time period varied in time asfollows, 5.75 s-9.25 s-5.75 s-9.25 s, an unacceptable amount of shotoverlap was found.

The systems and methods of the invention may be used in many spreadembodiments. For example, for obtaining deghosted seismic data, it maybe possible to provide one or more seismic streamers with a companionseismic streamer where the companions are towed in over/under fashion.The vertical distance between seismic streamers in an over/under seismicstreamer pair may range from 1 meter to 50 meters, and may be about 5meters. A selected number of hydrophones, either mounted within theseismic streamer or in/on equipment mounted onto the seismic streamer,may be used as receivers in an acoustic ranging system and therebyprovide knowledge of the horizontal, vertical and inline position ofCOSAs as well as seismic streamers.

In use, systems and methods of the invention are particularly adept for3D and so-called 4D marine seismic data acquisition surveys. Morespecifically, the systems and methods of the invention may be integratedinto the seismic towing vessel steering strategy, and may be integratedinto positioning strategies for spread elements other than seismicsources. In time-lapse or so-called 4D seismic, the source and receiversmay be positioned to within a few meters of a baseline survey in orderto gather a good picture of the evolution of a reservoir over time. Thegeophysical requirement for the accuracy of the repositioning varieswith the geological structure and the expected time-difference signal,but generally a 10 meter positioning discrepancy is allowed, and often abigger mismatch is allowed due to practicalities regarding thehistorical repositioning abilities. It is desired to position the sourceto within 5 meters, and the streamers to within about 10 meters of theirprevious tracks. Computing a residual difference between the 3Dcoordinate position and a pre-plot 3D coordinate position of a COS orCOSA point may be helpful in order to meet these targets as it allowsfor corrective actions to be taken before it is too late. One use ofsystems and methods of the invention is to make approximate inlinepositioning of COSAs by using controllable actuators, and to fine tuneby use of compensation devices such as those described in reference toFIGS. 6A and 6B.

Systems and methods of the invention may interact with any number ofspread control elements, which may include one or more orientationmembers, a device capable of movements that may result in any one ormultiple straight line or curved path movements of a spread element in3-dimensions, such as lateral, vertical up, vertical down, horizontal,and combinations thereof. The terms and phrases “bird”, “cablecontroller”, “streamer control device”, and like terms and phrases areused interchangeably herein and refer to orientation members having oneor more control surfaces attached thereto or a part thereof. A“steerable front-end deflector” (or simply “deflector”) such astypically positioned at the front end of selected streamers, such as 16and 18 in the figures, and other deflecting members, such as those thatmay be employed at the front end of seismic sources or source arrays,may function somewhat to influence inline skew, although their purposeis primarily to correct for crossline and depth positions. Orientationmembers are primarily used to pull streamers and steer sources laterallywith respect to direction of movement of a tow vessel. Horizontalseparation between individual source strings may range from about 10 toabout 100 meters, and the horizontal or crossline source stringseparation may be consistent between one source string and its nearestneighbors. Horizontal and/or vertical control of streamers may beprovided by orientation members which may be of any type as explainedherein, such as small hydrofoils or steerable birds that can provideforces in the vertical and/or horizontal planes. One suitableorientation member is the device known under the trade designationQ-FIN™, available from WesternGeco LLC, Houston, Tex., and described inU.S. Pat. No. 6,671,223, describing a steerable bird that is designed tobe electrically and mechanically connected in series with a streamer;another suitable device is that known under the trade designationDigiBIRD™, available from Input/Output, Inc., Stafford, Tex. Otherstreamer positioning devices, such as the devices described in U.S. Pat.Nos. 3,774,570; 3,560,912; 5,443,027; 3,605,674; 4,404,664; 6,525,992and EP patent publication no. EP 0613025, may be employed.

Systems of the invention may communicate with the outside world, forexample another vessel or vehicle, a satellite, a hand-held device, aland-based device, and the like. The way this may be accomplished variesin accordance with the amount of energy the system requires and theamount of energy the system is able to store locally in terms ofbatteries, fuel cells, and the like. Batteries, fuel cells, and the likemay be employed, and wireless communication may be sufficient.Alternatively, or in addition, there may be a hard-wire power connectionand a hard wire communications connection to another device, this otherdevice able to communicate via wireless transmission.

Certain systems and methods of the invention may work in feed-forwardedfashion with existing control apparatus and methods to position not onlythe seismic sources, but streamers as well. Sources and streamers may beactively controlled by using GPS data or other position detector sensingthe position of the COSA or streamer (e.g. underwater acoustic network),or other means may sense the orientation of one or more COSAs orindividual streamers (e.g. compass) and feed this data to navigation andcontrol systems. While gross positioning and local movement of center ofsource and/or streamer front end center may be controlled viacontrolling the actuators and controllers herein described, fine controlmay be accomplished on some other vessel, locally, or indeed a remotelocation. By using a communication system, either hardwire or wireless,environmental information ahead of the vessel may be sent to one or morelocal controllers, as well as the controllers of systems of theinvention. The local controllers may in turn be operatively connected tospread control elements comprising motors or other motive power means,and actuators and couplers connected to the orientation members (flaps),and, if present, steerable birds, which function to move the spreadcomponents as desired. This in turn may adjust the position of a spreadelement or COSA, causing it to move as desired. Feedback control may beachieved using local sensors positioned as appropriate depending on thespecific embodiment used, which may inform the local and remotecontrollers of the position of one or more COSAs, crossline distancebetween source arrays and streamers, a position of an actuator, thestatus of a motor or hydraulic cylinder, the status of a steerable bird,and the like. A computer or human operator can thus access informationand control the entire positioning effort, and thus obtain much bettercontrol over the seismic data acquisition process.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims. In the claims, no clauses are intended to be inthe means-plus-function format allowed by 35 U.S.C. § 112, paragraph 6unless “means for” is explicitly recited together with an associatedfunction. “Means for” clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, althoughelectronic and hydraulic motion platforms may not be structuralequivalents in that an electronic motion platform employs one type ofactuator, whereas a hydraulic motion platform employs a different typeof actuator, in the environment of movable platforms, electronic andhydraulically actuated movable platforms may be equivalent structures.

1. A system comprising: (a) a marine seismic spread comprising a towingvessel and a seismic source, the seismic source comprising one or moresource arrays each having a center of source array, each source arrayhaving one or more source strings; (b) a seismic source deploymentsub-system on the towing vessel, the sub-system controlled by acontroller including a software module, the software module and thedeployment sub-system adapted to control an inline distance between oneof the centers of source array and a target coordinate.
 2. The system ofclaim 1 wherein one or more seismic streamers are towed by the towingvessel, or a separate towing vessel.
 3. The system of claim 1 whereinthe seismic source deployment sub-system comprises one or more actuatorsselected from winches, capstans, and the like.
 4. The system of claim 3wherein the individual source strings in a source array are actuatedpneumatically or electronically through individual active cables woundor unwound from winches.
 5. The system of claim 3 wherein the port winchmay be wound a substantially similar amount as the starboard side winchis unwound, or vice versa.
 6. The system of claim 1 wherein the sourcedeployment sub-system comprises both active source tow members andpassive steering tow members.
 7. The system of claim 6 wherein thelength of active source tow members are not controlled but are allowedto move inline, while a set of separate passive tow members areconnected either to the active tow members or the sources themselves,and the passive tow members do not actuate the sources, but their inlinelengths are controlled by separate deployment systems to control aninline distance between one of the centers of source array and a targetcoordinate.
 8. The system of claim 1 wherein the seismic sourcedeployment sub-system comprises one or more movable actuators, whereinthe actuators ride on one or more movable platforms on the vessel. 9.The system of claim 8 wherein the software module controls both themovable platform and the actuators.
 10. The system of claim 1 comprisingheave compensators, whereby the length of either active source towmembers or passive steering tow members are adjusted by exerting a forceon the tow member.
 11. The system of claim 1 wherein the seismic sourcedeployment sub-system is load-balanced.
 12. The system of claim 1wherein the controller and software module are physically a part of theseismic source deployment sub-system.
 13. The system of claim 1 whereinthe controller is selected from PI, PD, PID, and MP controllers andcomputes a residual equal to a difference between a target point 3Dcoordinate COSA position and an actual COSA position, optionallytogether with current and wind measurements, to produce one or moreinputs to one or more cable deployment actuators, which may be electricmotors, used by the seismic source deployment sub-system to control thesource inline positions using winches, motorized capstans, and the like.14. The system of claim 13 wherein the controller computes the residualcontinuously or non-continuously.
 15. The system of claim 14 wherein thecontroller comprises one or more specialized control strategies selectedfrom feed forward, cascade control, internal feedback loops, modelpredictive control, neural networks, and Kalman filtering techniques.16. The system of claim 1 comprising a seismic spread comprising one ormore vessels such as towing vessels, a chase vessel, a work vessel, oneor more a seismic sources, and optionally one or more seismic streamerstowed by towing vessels.
 17. The system of claim 16 wherein thestreamers and sources are separately towed or towed by the same vessel.18. The system of claim 1 used in conjunction with systems selected fromacoustic ranging networks, GPS, and other position sensors.
 19. A systemcomprising: (a) a marine seismic spread comprising a towing vessel and aseismic source, the seismic source comprising one or more source arrayseach having a center of source array, each source array having one ormore source strings; (b) means for deployment of a seismic source fromthe towing vessel, the means for deployment adapted to control an inlinedistance between one of the centers of source array and a targetcoordinate.
 20. A method comprising: (a) measuring a position of acenter of a marine seismic source in a marine seismic spread; (b)computing a residual difference between the measured position and atarget position of the center of source; and (c) steering the sourceusing a seismic source deployment sub-system comprising one or more towmembers attached to the source, the tow members adjusted based on theresidual difference.
 21. The method of claim 20 wherein the seismicdeployment sub-system comprises one or more motorized actuators that areload balanced.
 22. The method of claim 20 including towing one or moreseismic streamers in over/under configuration, “V” configuration, “W”configuration, or some other configuration.
 23. The method of claim 20wherein the computing a residual comprises computing a residual for aninline distance between two centers of source arrays.